1. Field of the Invention
This invention relates generally to implantable cardiac rhythm management devices, and more particularly to a method for establishing an optimum pacing mode and delay parameters for multiple pacing sites in a dual chamber implantable programmable pacemaker.
2. Related Art
An earlier patent to Baumann, a co-inventor herein, U.S. Pat. No. 4,800,471, assigned to the assignee of the present invention, the teachings of which are hereby incorporated by reference, explains that cardiac pacing can be used to improve hemodynamics in congestive heart failure (CHF) patients. One recognized and accepted indication of hemodynamic performance is reflected in the patient""s pulse pressure (PP) which is defined as the difference between systolic aortic pressure and diastolic aortic pressure. PP could be used to optimize the pacing parameters in applying CHF therapy, however, this would require the use of a suitably positioned pressure sensor.
The Baumann ""471 patent recognizes that an indirect indication of PP can be derived from the patient""s atrial cycle length (ACL), which is the duration of the interval between consecutive P-waves in an ECG signal. The earlier Baumann patent discloses a method for using ACL to optimize CHF therapy parameters that involves looking at a transient sequence in which, after a period of intrinsic cardiac activity, a short predetermined sequence of pacing stimuli is delivered to the patient""s heart. Any subsequent transient increase in measured ACL provides an indication of the therapy""s effectiveness over intrinsic cardiac activity. Likewise, a subsequent transient decrease in measured ACL is indicative that the pacing therapy is non-beneficial.
In applying the methodology to an implantable, microprocessor-based controller of the type typically used in a programmable dual-chamber pacemaker, the device is made to cycle through transient paced beats with different pacing mode and AV delay configurations. Each such configuration is defined to be a group of consecutive beats with the same paced AV delay and the same pacing mode (right ventricular, left ventricular or bi-ventricular pacing). Each of the configurations is immediately preceded by a group of baseline beats. In the disclosed arrangement, three different pacing modes and five different AV delays are used, with each such delay being shorter than a previously measured value of the intrinsic AV delay. The particular mode/AV delay combination that results in the largest increase in ACL is then programmed into the pacemaker to thereby optimize hemodynamic performance of the patient""s heart. To avoid inaccuracies due to noise, the algorithm described in the Baumann ""471 patent is made to vary the order of therapy; randomization and averaging techniques are then used to extract data from repeated tests.
While the above approach has proved to be a useful tool, it does not take into account variations in time between pulse events with respect to pacing at multiple sites. It is common to stimulate both ventricle chambers, for example, and particularly the left ventricle can be provided with a plurality of sequentially paced sites. Each of these is operated using a timed delay sequence which may be selected from a menu of sequence timings which itself may change as data regarding patient history accumulates. Thus, if all paced sites could be integrated into an optimal pacing rhythm, additional benefit could be accorded the patient.
The foregoing features and advantages of the invention are achieved by providing an improved method for optimizing the inter-site delay and pacing mode configuration of an implanted, programmable pacemaker when treating CHF patients. The pacemaker involved is of the dual chamber type that includes an atrial sense circuit, a ventricular sense circuit and a pulse generator for applying cardiac stimulating pulses selectively to the right ventricular chamber, the left ventricular chamber or both chambers sequentially (bi-ventricular pacing). A plurality of pacing sites may be located in a single chamber, usually the left ventricle, and these are also paced using a time variable delay sequence.
The patient""s intrinsic atrial depolarization events are tracked and from such events the ACL is measured over a first predetermined number of heartbeats, N1, to establish a baseline value. At least one of the inter-site delay interval and the pacing mode configuration is changed for a predetermined number of stimulated heartbeats, N2 and, again, the ACLs between successive paced beats is measured. These steps are repeated in iterative cycles until all of the preprogrammed inter-site delay intervals and ventricular chamber options have been utilized.
Subsequently, a comparison is made to determine which configuration of pacing mode and inter-site delay values resulted in the maximum increase ACL and those values are then programmed into the pacemaker. In that maximum increase of ACL correlates with maximum increase of PP, hemodynamic performances are thereby optimized. Additional performance parameters may also be used to correlate to PP or other relevant indicators of cardiac performance, these performance parameters include: ventricular volumes, blood flow velocity, total acoustic noise, and direct measurement of pressure.
As used herein, the terms xe2x80x9csite-to-site delayxe2x80x9d and xe2x80x9cinter-site delayxe2x80x9d mean the time interval between any sequential pacing events in the same cardiac cycle regardless of whether they occur in different or the same chamber. Thus, AV, Vxe2x80x94V, V1-V2 (same chamber), Axe2x80x94A etc. may be represented depending on the pacing configuration.
The optimization determination is first made with the patient at rest to determine the most advantageous pacing mode. Thereafter, a one or more additional or periodic determinations can be implemented with the patient exercising or otherwise in an active state employing the technique to determine the optimum site-to-site delays and enable dynamic site-to-site delays to be implemented based on activity level. This empowers the system to implement dynamic site-to-site delays on its own based on an internal monitoring system.